This invention relates to the manufacture of asphalt roofing shingle pieces, and in particular, the use of processed volcanic ash to maintain separation of the finished roofing shingles and prevent the transfer of shingle coloring agents from one shingle to another.
Asphalt roofing shingles are composed of an organic material base or fiberglass core to which a coating of hot asphalt is applied. Different colored shingles are made by coating the hot asphalt covered core with a coloring agent. The shingles are cooled in a stream of water and cut into the desired shingle shape. This results in an asphalt shingle which can then be applied to a roof. One problem with this basic construction process is the tendency of the finished shingles to adhere together under heat or pressure. This can result in multiple shingles being glued together by the asphalt. These shingles may not be separable without causing damage to the shingles.
Asphalt roofing shingles, after manufacture, are generally packaged into 33 square foot units weighing more than 70 pounds. These packages of shingles are stacked onto pallets for shipping. If the shingles are shipped by railroad, one pallet is commonly stacked on another to fill the railroad car. This packaging, palleting and shipping produces substantial pressure on the shingles and can result in the asphalt coating adhering to adjoining shingles. The shingles also can be affected by high temperatures found in shipping containers during warm weather. Temperatures of 150.degree. degrees Fahrenheit can be attained in a railroad shipping car during warm whether.
The coloring of the asphalt shingle is applied to the upper surface of the shingle by spraying color nodules on to the surface of the hot asphalt. This color, however, is susceptible to transferring to the bottom of the adjoining shingle during the above-described pressure and high temperature found in the shipping of the shingles.
Therefore, it is necessary to include a separating or parting agent on the finished shingles in order to keep the finished shingles separate from one another and to prevent color transfer from one shingle to the adjoining shingle. The ideal separating or parting agent would be inexpensive, exhibit 100% adhesion to the hot asphalt, be resistant to removal during water cooling of the hot asphalt, not contribute any respirable dust to the work place atmosphere, and not dull the knives used to cut the asphalt material into shapes.
A number of agents commonly have been used to accomplish separation of asphalt roofing shingles among these are talc, mica-containing material and crystalline silica or sand. While each of these agents is capable of providing separation of asphalt shingles, they each present a several undesirable characteristics in varying degrees. These drawbacks include cost, poor color transfer prevention, dulling of cutting knives, work place pollution, and respirable dust danger.
Talc, a form of hydrous magnesium silicate (Mg.sub.3 SiO.sub.10 (OH).sub.2, is usually the main constituent of mixtures offered commercially as talc. Talc is relatively expensive with respect to the other separating agents. However, the effectiveness of talc in maintaining color separation has been found to diminish significantly over a two week period when subjected to train box-car storage conditions of approximately 150.degree. F. and the pressures developed in a two pallet-high roofing shingle stack. Talc also creates a significant dust and pollution problem. When talc is sprayed on the hot asphalt shingle, only a portion of the talc achieves contact with the asphalt and a portion falls away onto the floor of the manufacturing site. This necessitates that workers be assigned to the cleanup of the talc from the floor. It is not uncommon for this task to require two full-time workers for a shingle plant. Talc also becomes airborne during spraying and cleanup. The presence of airborne talc requires that workers wear respiratory equipment as the threshold limit value (TLV) for talc is 2 mg talc per cubic meter of air under OSHA and Mine Safety and Health Administration regulations. Finally, talc is washed from the shingles during the water cooling process and mixes with the wash water. The talc polluted wash water must then be collected in ponds or tanks to allow the talc to settle-out before reuse or discharge of the cooling water. The talc must be collected from the ponds or tanks and carted to a waste site. Thus the cost of using talc to maintain shingle separation is further increased by the related industrial hygiene costs of talc. The advantage to talc is its softness which minimizes dulling of the shingle-cutting knife blades. Dulling of these blades and their replacements is costly as the shingle line must be stopped while the blades are removed and replaced.
An alternative separation product is sand, a form of crystalline silica. The sand is dried and screened and then sprayed on to the hot asphalt shingles before cooling. Sand is subject to many of the same industrial hygiene problems and associated costs as talc. Sand is initially cheaper to purchase, however, it also falls off from the shingles after it is applied and washes off during the water cooling process. This results in the need to clean sand from the floors and to clean cooling water and water holding ponds and tanks. The cleanup and application of sand can also inject respirable crystalline silica into the work atmosphere. This may require workers to wear respirators as crystalline silica is a Class A carcinogen. Sand also is extremely hard on the shingle cutting blades. Use of sand as a parting agent results in cutting blade replacement approximately 15 times more frequently than talc.
Another alternative is to use micaceous material as the parting agent. This material also presents the dust problems of talc and sand and the polluting of the cooling water. Micaceous materials also dull the shingle cutting knives and necessitates blade replacement approximately eight times as often as when talc is used as the parting agent.